Liquid crystal matrix display panels possess certain significant advantages over CRT displays, with regard to low power consumption, thin shape, and potentially low manufacturing cost. However although liquid crystal displays are now in widespread use for such applications are wristwatch and portable calculator displays, large-size liquid crystal matrix display panels have not yet been produced in very substantial amounts. Such large-size liquid crystal matrix display panels could replace the CRT displays used in television receivers, computer terminals, etc, i.e. could display graphic or pictorial information, while bringing all the advantages of liquid crystal devices to such applications, including the important capability for operating with a very low level of supply voltage.
In general, it is necessary to provide some form of interface circuitry between a source of display data and the display device itself, i.e. to apply suitable drive signals in accordance with the display data to the display device. Moreover, if the rate of generation of the display data is different from the speed of operation of the display device, then it will be necessary to provide some form of memory means to temporarily store the display data before it is transferred to the display device. In the case of television reception, the duration of each horizontal scanning period (i.e. the period between successive horizontal sync pulses in the video signal) is equal to the time during which the CRT trace sweeps out a horizontal line of the displayed image. In this case, therefore, since the rate of input of the video data can be made equal to the speed of operation of the display device, it is not necessary to provide video data memory means. However in general, prior art drive methods for applying display data such as television video signals to a liquid crystal matrix display panel operate such that the speed of operation of the display panel is lower than the rate of input of video data, i.e. line-by-line scanning of rows of display elements in synchronism with the horizontal scanning periods of the video signal is not possible. Thus with such prior art drive methods it is necessary to provide video memory circuits in order to match the speed of operation of the liquid crystal matrix display panel to the rate of input of the video data. This is essentialaly due to the fact that it has hitherto been difficult to attain a sufficiently high degree of contrast using liquid crystal matrix display panels having a very large number of display elements such as is required to display a television image.
This limitation on display element number due to display contrast consideration is essentially determined by the number of electrodes of the liquid crystal matrix display panel to which periodic scanning pulses are applied, as described in detail hereinafter. With the drive method of the present invention, the effective number of these electrodes for a given number of display elements can be greatly reduced, e.g. to one-half or one-third, without a reduction in display contrast. The drive method of the present invention therefore makes it possible to produce low-cost, low power-consumption liquid crystal matrix display systems which can directly replace CRT displays in such applications as television or computer graphic displays, utilizing simple peripheral interface circuits and with no necessity to provide large-capacity video data storage means.